I defer to those currently at USNA for the current rules. However, one thing you learn in the military is to plan for the unexpected. Thus, many mids and, later, officers, plan to arrive back from leave many hours or even days early, especially if traveling long distances or during times of typical bad weather.
During my time in the military, you got in big trouble if you missed movement, deployment, etc. They might cut you some slack if the reason was totally beyond your reasonable ability to preduct and/or account for. To take an example from today, if you were traveling in Thailand, planned to arrive back two days prior to your planned deployment/commitment, and were stuck in Thailand by the airport protestors, ok. Reason: planning to return from overseas 2 days early demonstrated that you planned for the "reasonably unexpected" and protestors blocking the airports for over a week was beyond your ability to preduct or account for. However, if you flew to CA and planned to arrive back at BWI at 3 pm when holiday leave expires at 6 pm, you'd be in trouble. Reason: you should have expected that there might be bad weather, crowds, traffic, etc. and only gave yourself a 2 hr cushion while coming 2,500 miles.
Proper prior planning prevents poor performance. Words to live by.
However, as noted, not sure what policy is today.